Switching regulators are widely used to provide voltage regulation in electronics sub-systems. A switching regulator may generate an output voltage by generating a pulse output from an input voltage. The pulse output is generally filtered by a low pass filter to generate a DC output voltage. The amplitude of the DC output voltage may be regulated by varying the pulse width of the pulses that comprise the pulse output or controlling the on-time or the off-time of the pulse output. A significant portion of the power losses in a switching regulator occur in the power switches that generate the pulse output from the input voltage. The power switch losses may be divided between conduction losses and switching losses. As the pulse width decreases in proportion to the switching frequency of the pulse output, the switching losses may increase relative to the conduction losses. In addition, at narrower pulse widths such as a 10% duty cycle, maintaining regulation of the output voltage may become more difficult resulting in increased error in the output voltage.
FIG. 1A shows an exemplary conventional voltage regulator 10 for converting an input voltage of 12 volts to an output voltage, Vout, of approximately 1.2 volts. A conduction switch 12 and freewheeling switch 14 may convert the input to a pulse output. The conduction switch 12 and freewheeling switch 14 are generally selected to be high voltage devices to withstand the entire input voltage. The pulse output may be filtered by an output inductor 16 and output capacitor 18 to form Vout. FIG. 1B shows waveforms associated with the conventional voltage regulator 10. Waveform 20 shows the operating state of the conduction switch 12. Waveform 22 shows the voltage, V1, across the freewheeling switch 14. Voltage V1 may typically have a rise time and a fall time of about 10 nsec. The rise time and fall time are typically limited by the type of switches used for the conduction switch 12 and the freewheeling switch 14. The switching losses may increase as the rise time and fall time increase. Waveform 24 shows the current, I1, flowing through the output inductor 16. As the pulse width continues to decrease, switching losses become a greater proportion of the total power losses.